Flow cells utilized in fluorometers have up till now been constructed out of quartz. Such cells require complicated fittings and seals which were costly and prone to leak. It has not been believed possible to substitute plastic materials for the quartz cells known in the art as it was believed that such plastic materials would be fluorescent in the desired ultraviolet region utilized in the fluorometer and thus would interfere with the measurement of the fluorescence of the sample passing through the flow cell.